The wireless portable Internet is a next-generation communication system that supports mobility in a LAN data communication system using a fixed access point such as the existing wireless LAN.
A variety of standards for the wireless portable Internet have been suggested, and the international standardization of portable Internet is current in progress, centering on the IEEE 802.16e.
FIG. 1 is a schematic of a wireless portable Internet system.
The wireless portable Internet system basically includes a mobile subscriber station (MSS) 10, base stations 20 and 21 performing wireless communication with the mobile subscriber station 10, routers 30 and 31 being connected to the base stations through a gateway, and an Internet network.
The conventional wireless LAN system such as IEEE 802.11 provides a data communication system capable of wireless communication in a local area centering on a fixed access point. But, the IEEE 802.16 has the limitation that it cannot provide mobility of the mobile subscriber station but simply supports wireless LAN data communication.
The IEEE 802.16, which is the standards for the MAN, refers to a data communication network for the intermediate area between LAN (Local Area Network) and WAN (Wide Area Network).
The wireless portable Internet system under development in the IEEE 802.16e group or the like secures mobility of the mobile subscriber station even when the mobile subscriber station 10 shown in FIG. 1 is moving from a cell managed by the base station 20 to a cell managed by the base station 21, thereby providing a seamless data communication service.
Therefore, the wireless portable Internet system supports a handover of the mobile subscriber station 10 as in the mobile communication service, and performs dynamic IP address allocation according to the movement of the mobile subscriber station.
The mobile subscriber station 10 and the base stations 20 and 21 in the wireless portable Internet system perform OFDMA (Orthogonal Frequency Division Multiple Access) communication. The OFDMA is a multiplexing method that combines the time division multiplexing (TDM) method and the frequency division method using a plurality of orthogonal frequency subcarriers as a plurality of sub-channels. The OFDMA is substantially strong against fading occurring on multi paths, and has a high data transfer rate.
The IEEE 802.16e employs the AMC (Adaptive Modulation and Coding) method that adaptively selects modulation and coding methods by request and acceptance.
FIG. 2 is a hierarchy chart showing the hierarchical structure of a wireless portable Internet system.
The hierarchical structure of the IEEE 802.16e wireless portable Internet system includes a physical layer L10, and MAC (Media Access Control) layers L21, L22, and L23.
The physical layer L10 has a wireless communication function such as modulation/demodulation, coding, and so forth as usually performed by a physical layer.
Unlike a wire Internet system, the wireless portable Internet system has a single MAC layer in charge of different functions rather than multiple layers classified by functions.
Regarding function-specific sublayers, the MAC layer includes privacy sublayer L21, MAC common part sublayer L22, and service specific convergence sublayer L23.
The service specific convergence sublayer L23 has a payload header suppression and QoS mapping function, in consecutive data communication.
The MAC common part sublayer L22 is the core part of the MAC layer that has functions of system access, bandwidth allocation, connection establishment and maintenance, and QoS control.
The privacy sublayer L21 has functions of equipment authentication and security key exchange, and encryption. The equipment authentication is performed only at the privacy sublayer L21; and the user authentication is performed at the upper layer (not shown) of the MAC layer.
FIG. 3 is a schematic diagram showing the connection between the base-station and the mobile subscriber station in the wireless portable Internet system.
The connection is provided between the MAC layer of the mobile subscriber station MSS and that of the base station BS.
The term “Connection C1” as used herein does not refer to a physical connection but a logic connection that includes a basic connection for MAC message transfer, two management connections, and a transport connection for traffic transfer by service flows. The mapping relationship between the MAC peers of the mobile subscriber station MSS and the base station BS includes one primary connection, one basic connection, one secondary management connection, and a plurality of transport connections provided as many as there are service flows.
Hence, the parameter/message as defined on the connection C1 refers to a function executed between the MAC peers. Actually, the parameter/message is processed into a frame, which is transferred through the physical layer and analyzed so as to enable the MAC layer to execute the function corresponding to the parameter/message.
The connection C1, which is established during the initial station registration, includes a basic connection used for MAC message transfer, and a management connection not sensitive to a delay but established during the initial subscriber registration. The management connection is divided into a primary management connection for managing a header for a lower layer, and a secondary management connection for managing a header for an upper layer.
The MAC message transported through the connection C1 includes a connection identifier (CID) used as an address of the MAC layer to identify the connection; a MAP defining the symbol offsets of bursts and sub-channel offsets time-divided by the mobile subscriber station on the downlink/uplink, the number of symbols of the resource allocated, and the number of sub-channels; and channel descriptors (including a DCD (Downlink Channel Descriptor) and a UCD (Uplink Channel Descriptor)) specifying the characteristic of the physical layer according to the characteristic of the downlink/uplink.
The MAC message also includes different messages of request (REQ), response (RSP), or acknowledgement (ACK) functions for various operations.
FIG. 4 is a frame diagram showing the frame structure of the wireless portable Internet system.
The frame is classified into a downlink frame F1 and an uplink frame F2 according to a transfer direction. In the frame diagram, the axis of the ordinate represents sub-channels comprising orthogonal frequencies while the axis of the abscissa represents the time-divided time axis.
The downlink frame F1 includes a preamble, a downlink MAP, an uplink MAP, and a plurality of downlink bursts. The downlink bursts are not subscriber-specific channels or resources, but transfer level specific channels or resources classified by transfer level having a same modulation method or a same channel skill.
The downlink MAP identifies a subscriber using the CID and has offset information, modulation method information, and coding information corresponding to the identified subscriber to allocate resources to the subscriber. The MAP has the characteristic of a broadcast channel and requires high robustness.
The uplink frame F2 has a function of user-specific transfer, and the uplink burst includes user-specific information.
FIG. 5 is a flow chart showing a connection establishment process in the wireless portable Internet system.
When the mobile subscriber station enters the cell of the base station, in step S1, the base station acquires downlink synchronization with the mobile subscriber station, in step S2. With the downlink synchronization acquired, the mobile subscriber station acquires an uplink parameter, in step S3. The parameter includes, for example, a channel descriptor message corresponding to the characteristic (e.g., signal-to-noise ratio) of the physical layer.
The ranging between the mobile subscriber station and the base station is achieved, in step S4. The ranging procedure is correcting and matching timing, power, and frequency information between the mobile subscriber station and the base station, and dividing into initial ranging and a subsequent periodic ranging.
After the completion of the ranging procedure, a negotiation of the basic capacity for connection establishment between the mobile subscriber station and the base station is performed, in step S5. Once the negotiation of the basic capacity is completed, the base station authenticates the mobile subscriber station using an equipment identifier such as the MAC address of the mobile subscriber station, in step S6.
When the mobile subscriber station is authenticated and authorized to use the wireless portable Internet service, the equipment address of the mobile subscriber station is registered, in step S8. Then, an IP address management system such as a DHCP (Dynamic Host Configuration Protocol) server provides an IP address to the mobile subscriber station to establish the IP connection, in step S8.
The mobile subscriber station receiving the IP address performs connection establishment for data transfer, in step S9.
FIG. 6 is a schematic of a conventional dynamic IP allocation system.
The IEEE 802.16 provides a handover function to a mobile subscriber station between base stations BS1 and BS2 so as to provide nobility to the existing fixed subscriber station.
However, the conventional standards not considering the handover (or called “handoff”) of the subscriber station sufficiently are problematic in that the session in use is disconnected during a handover of the subscriber station using a dynamic IP.
As illustrated in FIG. 6, upon receiving a dynamic IP address in the cell of the base station 20, the mobile subscriber station 10 requests the DHCP (Dynamic Host Configuration Protocol) of the base station 20. DHCP server 50 allocates a dynamic IP address to the mobile subscriber station 10 in response to the request of the mobile subscriber station. When receiving an IP address of “129.253.250.0” franc the DHCP server, for example, the mobile subscriber station 10 sets the IP address during an IP leasing period to communicate with a terminal node 40.
When the mobile subscriber station 10 moves to the cell of the base station 21 for handover, DHCP server 51 allocates a new IP address to the mobile subscriber station 10. In this case, the terminal node 40 cannot know the new IP address of the mobile subscriber station 10, so the session between the mobile subscriber station 10 and the terminal node 40 is disconnected.
In case of using a mobile IP for seamless service, a dynamic address allocation procedure is necessary during the mobile IP registration process as specified in the mobile IP standards, RFC3344. However, the existing IEEE 802.16e standards, where the connection to the MAC layer for dynamic address allocation using the mobile IP is not established, cannot support the seamless service. Accordingly, the wireless portable Internet subscriber cannot receive seamless service when using a dynamic IP address, thereby restraining the mobility of the subscriber-station.